Coating agent comprising at least four components, method for producing same, and use thereof

ABSTRACT

A coating composition consisting of at least four components, comprising a component (I) comprising at least one oligomeric or polymeric resin containing functional groups which react with isocyanate groups, as binder (A), a component (II) comprising at least one polyisocyanate as crosslinking agent (F), a component (III) which comprises water and is substantially free from acrylate copolymers (A) dispersed or dissolved therein, and a finely divided solid component (IV) which comprises at least one water-soluble or -dispersible finely divided solid acrylate copolymer (A); and also a process for producing a coating from a coating composition consisting of at least four components, which involves (1) mixing at least one component (I) with at least one component (II), to give the mixture (I/II); (2) mixing at least one component (III) with at least one finely divided solid component (IV), to give the mixture (III/IV); and then either (3) dispersing and/or dissolving the mixture (I/II) in the mixture (III/IV) or (4) dispersing and/or dissolving the mixture (III/IV) in the mixture (I/II); applying the resulting mixture (I/II/III/IV) to the surface that is to be coated, and curing the wet film.

The present invention relates to a coating composition consisting of atleast four components, comprising a component (I) comprising at leastone oligomeric or polymeric resin containing functional groups whichreact with isocyanate groups, as binder (A), a component (II) comprisingat least one polyisocyanate as crosslinking agent (F), and a component(III) which comprises water. The present invention additionally relatesto a process for preparing these coating compositions and also to theuse of the coating compositions in automotive OEM finishing, refinish,and for the coating of plastics, and also as topcoat materials orprimer-surfacers.

Coating compositions of the abovementioned type in which component (III)contains no binders (A) are known from the patent U.S. Pat. No.5,466,745. One of their uses is to produce clearcoats. The surfaces ofthese clearcoats, however, are still unable to satisfy every qualityrequirement, since they have pinholes and blisters.

Coating compositions of the abovementioned type in which component (III)comprises dissolved or dispersed binders (A) are known from the Germanpatents DE-A-195 42 626 and DE-A-44 21 823. These known coatingcompositions already have comparatively few surface problems, such aspopping marks or structuring, and as regards gloss, relaxation, sprayingreliability, fullness, weathering stability, and other importanttechnological properties they possess a good profile of properties.

The increasingly more stringent requirements of the market, however, aremaking it necessary to improve these known coating compositions stillfurther in terms of their homogeneity, stability, handling, and poppinglimits. Moreover, the solvent content is to be lowered further than hasbeen possible to date. Furthermore, the resulting coatings should havean even higher gasoline resistance and an even lower gray haze.

These known coating compositions or their component (III) comprisebinders in dispersion or solution in water, which in the dissolved ordispersed state, especially on prolonged storage, are infested anddestroyed by microorganisms, thereby rendering the component (III) inquestion of the coating compositions unusable and requiring disposal,which is a grave disadvantage both technically and economically.

If the component (III) affected is used anyway, it produces coatings,especially clearcoats, which are no longer in accordance with userrequirements, especially in the automobile industry.

It is an object of the present invention to find a novel coatingcomposition which no longer has the disadvantages depicted above butwhich instead is infested to a considerably reduced extent, if at all,by microorganisms and therefore has a relatively high storage stabilityof the component in question, with the advantageous properties of theknown coating compositions being at least retained if not indeedimproved further.

The invention accordingly provides the novel coating compositionconsisting of at least four components, comprising

(I) a component comprising at least one oligomeric or polymeric resincontaining functional groups which react with isocyanate groups, asbinder (A).

(II) a component comprising at least one polyisocyanate as crosslinkingagent (F),

(III) a component which comprises water and is substantially free fromacrylate copolymers (A) dispersed or dissolved therein, and

(IV) a finely divided solid component which comprises at least onewater-soluble or -dispersible finely divided solid acrylate copolymer(A).

In the text below, the novel coating composition consisting of at leastfour components is referred to for the sake of brevity as the “coatingcomposition of the inventions”.

The present invention further provides a process for preparing thecoating compositions of the invention, and also provides for their usein automotive OEM finishing, refinish, and the coating of plastics, astopcoat materials or primer-surfacers.

The coating compositions of the invention are notable, surprisingly, fora profile of properties which is improved over the prior art in relationin particular to the gloss, fullness, low popping tendency, sprayingreliability, and leveling, and also in respect of the weatheringstability.

The particular advantage of the coating composition of the invention isfirstly that component (III) is substantially-free from dissolved ordispersed acrylate copolymers (A), so that even on prolonged storage itis no longer infested by microorganisms, or only to an extent which doesnot perceptibly impair its performance properties. Secondly, theparticular advantage of the coating compositions of the invention isthat component (IV) may be stored for a particularly long time withoutdetriment to its performance properties. Furthermore, as a finelydivided solid, it can be added to the coating composition, especially tocomponent (III), in a particularly simple and easy fashion.

It is surprising, furthermore, that the coating compositions of theinvention comprising said at least four components may be preparedsimply by mixing without the need for complicated mixing and/ordispersing apparatus as described, for example, in the German patentDE-A-195 10 651. The coating compositions of the invention are thereforesuitable in particular for the field of automotive refinish, since theycan be prepared by the painter by simple mixing of the componentsdirectly prior to their application and can be cured at lowtemperatures.

A further advantage is that the coating compositions of the inventionprepared from said at least four components contain only a smallfraction of volatile organic solvents, despite the fact that the coatingcompositions are prepared using crosslinkers and binders dispersedand/or dissolved in organic media.

Moreover, the coating compositions of the invention ensure a high levelof variability, since it is possible to use not only the crosslinkingagents, pigments and additives that are recommended for aqueous coatingcompositions but also those used in conventional systems.

Finally, a feature of the inventive components of the coatingcompositions of the invention is a very good storage stability, whichcorresponds to that of conventional coating compositions.

The constituent of the coating composition of the invention that isessential to the invention is its finely divided solid component (IV),which comprises at least one water-soluble or -dispersible finelydivided solid acrylate copolymer (A).

The finely divided solid acrylate copolymers (A) for use in accordancewith the invention are oligomeric or polymeric resins containingfunctional groups which react with isocyanate groups.

Examples of suitable functional groups for use in accordance with theinvention that react with isocyanate groups are epoxy, amino, thioand/or hydroxyl groups, of which the hydroxyl groups are particularlyadvantageous and are therefore particularly preferred in accordance withthe invention.

Accordingly, the finely divided solid acrylate copolymers (A) which arepreferred in accordance with the invention comprise hydroxyl-containingoligomeric or polymeric resins.

Besides the hydroxyl groups, the finely divided solid acrylatecopolymers (A) may contain other functional groups as well, such asacryloyl, amide, imide, carbonate or epoxide groups.

In accordance with the invention, the finely divided solid acrylatecopolymers (A), viewed per se, are dispersible or soluble in water.

Examples of suitable water-soluble or water-dispersible finely dividedsolid acrylate copolymers (A) contain alternatively

(i) functional groups which can be converted into cations byneutralizing agents and/or quaternizing agents, and/or cationic groups,

or

(ii) functional groups which can be converted into anions byneutralizing agents, and/or anionic groups,

and/or

(iii) nonionic hydrophilic groups.

Examples of suitable functional groups (i) for use in accordance withthe invention that can be converted into cations by neutralizing agentsand/or quaternizing agents are primary, secondary or tertiary aminogroups, secondary sulfide groups or tertiary phosphine groups,especially tertiary amino groups or secondary sulfide groups.

Examples of suitable cationic groups (i) for use in accordance with theinvention are primary, secondary, tertiary or quaternary ammoniumgroups, tertiary sulfonium groups or quaternary phosphonium groups,preferably quaternary ammonium groups or tertiary sulfonium groups, butespecially tertiary sulfonium groups.

Examples of suitable functional groups (i) for use in accordance withthe invention that may be converted into anions by neutralizing agentsare carboxylic acid, sulfonic acid or phosphonic acid groups, especiallycarboxylic acid groups.

Examples of suitable anionic groups (i) for use in accordance with theinvention are carboxylate, sulfonate or phosphonate groups, especiallycarboxylate groups.

Examples of suitable nonionic hydrophilic groups (i) for use inaccordance with the invention are polyether groups, especiallypoly(alkylene ether) groups.

Regarding the preparability, handling and particularly advantageousproperties of the coating compositions of the invention prepared usingthem, the finely divided solid acrylate copolymers (A) which contain theanion-forming groups and/or anions (ii), especially the carboxylic acidand/or the carboxylate groups, afford very particular advantages, and soare used with very particular preference in accordance with theinvention.

Examples of very particularly, preferred finely divided solid acrylatecopolymers (A) of the last-mentioned type, for use in accordance withthe invention, are

(A1) the acrylate copolymers (A1) which are described below, containhydroxyl groups and carboxylic acid and/or carboxylate groups, and havea number average molecular weight Mn of between 1000 and 30,000 daltons,an OH number of from 40 to 200 mg KOH/g, and an acid number of from 5 to150 mg KOH/g.

Owing to their comparatively simple preparation, their easy handling,their advantageous profile of properties, and the particular advantagesof the coating compositions of the invention produced using them, veryparticular preference is given to using the finely divided solidacrylate copolymers (A1). Moreover it is found in many cases that theproblems of infestation by microorganisms can be solved substantiallyand in many cases even completely simply by using the acrylatecopolymers (A1) in finely divided solid form.

Suitable finely divided solid acrylate copolymers (A1) include allacrylate copolymers having the stated OH numbers, acid numbers,molecular weights, and viscosities.

In particular, use is made of finely divided solid acrylate copolymers(A1) obtainable in the presence of at least one polymerization initiatorby bulk polymerization, solution polymerization in an organic solvent orsolvent mixture, by emulsion polymerization or precipitationpolymerization in water of

a1) a (meth)acrylic ester which is substantially free from acid groupsand is different from but copolymerizable with (a2), (a3), (a4), (a5),and (a6), or a mixture of such monomers (a1),

a2) an ethylenically unsaturated monomer which carries at least onehydroxyl group per molecule and is substantially free from acid groups,and which is copolymerizable with (a1), (a3), (a4), (a5), and (a6) butdifferent from (a5), or a mixture of such monomers (a2,

a3) an ethylenically unsaturated monomer which carries per molecule atleast one acid group which can be converted into the corresponding acidanion group, and which is copolymerizable with (a1), (a2), (a4), (a5),and (a6), or a mixture of such monomers (a3), and

a4) if desired, one or more vinyl esters of alpha-branchedmonocarboxylic acids having from 5 to 18 carbon atoms per molecule,and/or

a5) if desired, at least one reaction product of acrylic acid and/ormethacrylic acid with the glycidyl ester of an alpha-branchedmonocarboxylic acid having from 5 to 18 carbon atoms per molecule, orinstead of the reaction product an equivalent amount of acrylic and/ormethacrylic acid which is then reacted during or after thepolymerization reaction with the glycidyl ester of an alpha-branchedmonocarboxylic acid having from 5 to 18 carbon atoms per molecule,

a6) if desired, an ethylenically unsaturated monomer which issubstantially free from acid groups, is copolymerizable with (a1), (a2),(a3), (a4), and (a5) but different from (a1), (a2), (a4), and (a5), or amixture of such monomers (a6),

the nature and amount of (a1), (a2), (a3), (a4), (a5), and (a6) beingselected so that the polyacrylate resin (A1) has the desired OH number,acid number, and molecular weight.

To prepare the finely divided solid acrylate copolymers (A1) it ispossible as component (a1) to use any (meth)acrylic alkyl or cycloalkylester which is copolymerizable with (a2), (a3), (a4), (a5), and (a6) andwhich has up to 20 carbon atoms in the alkyl radical, especially methyl,ethyl, propyl, n-butyl, sec-butyl, tert-butyl, hexyl, ethylhexyl,stearyl and lauryl acrylate or methacrylate; cycloaliphatic(meth)acrylic esters, especially cyclohexyl, isobornyl,dicyclopentadienyl, octahydro-4,7-methano-1H-indene-methanol ortert-butylcyclohexyl (meth)acrylate; (meth)acrylic oxaalkyl esters oroxacycloalkyl esters such as ethyl triglycol (meth)acrylate andmethoxyoligoglycol (meth)acrylate having a molecular weight Mn ofpreferably 550; or other ethoxylated and/or propoxylated, hydroxyl-free(meth)acrylic acid derivatives. These may contain minor amounts of(meth)acrylic alkyl or cycloalkyl esters of higher functionality, suchas ethylene glycol, propylene glycol, diethylene glycol, dipropyleneglycol, butylene glycol, 1,5-pentanediol, 1,6-hexanediol,octahydro-4,7-methano-1H-indenedimethanol or 1,2-, 1,3- or1,4-cyclohexanediol di(meth)acrylate; trimethylolpropane di- ortri(meth)acrylate; or pentaerythritol di-, tri- or tetra(meth)acrylate.In the context of the present invention, minor amounts of monomers ofrelatively high functionality are understood as being amounts which donot lead to crosslinking or gelling of the polyacrylate resins.

As component (a2) it is possible to use ethylenically unsaturatedmonomers which carry at least one hydroxyl group per molecule and aresubstantially free from acid groups, and are copolymerizable with (a1),(a2), (a3), (a4), (a5), and (a6) but different from (a5), such ashydroxyalkyl esters of acrylic acid, methacrylic acid or anotheralpha,beta-ethylenically unsaturated carboxylic acid which are derivedfrom an alkylene glycol which is esterified with the acid or areobtainable by reacting the acid with an alkylene oxide, especiallyhydroxyalkyl esters of acrylic acid, methacrylic acid, ethacrylic acid,crotonic acid, maleic acid, fumaric acid or itaconic acid in which thehydroxyalkyl group contains up to 20 carbon atoms, such as2-hydroxyethyl, 2-hydroxypropyl, 3-hydroxypropyl, 3-hydroxybutyl,4-hydroxybutyl acrylate, methacrylate, ethacrylate, crotonate, maleate,fumarate or itaconate; 1,4-bis(hydroxymethyl)cyclohexane,octahydro-4,7-methano-1H-indenedimethanol, or methylpropanediolmonoacrylate, monomethacrylate, monoethacrylate, mono-crotonate,monomaleate, monofumarate or monoitaconate; or reaction products ofthese hydroxyalkyl esters and cyclic esters, such asepsilon-caprolactone, for example; or olefinically unsaturated alcoholssuch as allyl alcohol or polyols such as trimethylolpropane monoallyl ordiallyl ether or pentaerythritol monoallyl, diallyl or triallyl ether.Regarding these monomers (a2) of higher functionality, the comments maderegarding the higher-functional monomers (a1) apply analogously. Thefraction of trimethylolpropane monoallyl ether is usually from 2 to 10%by weight, based on the overall weight of the monomers (a1) to (a6) usedto prepare the polyacrylate resin. In addition, however, it is alsopossible to add from 2 to 10% by weight, based on the overall weight ofthe monomers used to prepare the polyacrylate resin, oftrimethylolpropane monoallyl ether to the finished polyacrylate resin.The olefinically unsaturated polyols, such as trimethylolpropanemonoallyl ether in particular, may be used as sole hydroxyl-containingmonomers, but in particular may also be used proportionally incombination with other of the hydroxyl-containing monomers mentioned.

As component (a3), it is possible to use any ethylenically unsaturatedmonomer which carries at least one acid group, preferably a carboxylgroup, per molecule and is copolymerizable with (a1), (a2), (a4), (a5),and (a6), or a mixture of such monomers. Acrylic acid and/or methacrylicacid are used with particular preference as component (a3). It is,however, also possible to use other ethylenically unsaturated carboxylicacids having up to 6 carbon atoms in the molecule. Examples of suchacids are ethacrylic acid, crotonic acid, maleic acid, fumaric acid, anditaconic acid. A further possibility is to use ethylenically unsaturatedsulfonic or phosphonic acids, and/or their partial esters, as component(a3). Further suitable components (a3) includemono(meth)acryloyloxyethyl maleate, succinate, and phthalate.

As component (a4) use is made of one or more vinyl esters ofalpha-branched monocarboxylic acids having from 5 to 18 carbon atoms inthe molecule. The branched monocarboxylic acids may be obtained byreacting formic acid or carbon monoxide and water with olefins in thepresence of a liquid, strongly acidic catalyst; the olefins may becracking products of paraffinic hydrocarbons, such as mineral oilfractions, and may contain both branched and straight-chain acylicand/or cycloaliphatic olefins. The reaction of such olefins with formicacid or with carbon monoxide and water produces a mixture of carboxylicacids in which the carboxyl groups are located predominantly on aquaternary carbon atom. Other olefinic starting materials are, forexample, propylene trimer, propylene tetramer, and diisobutylene.Alternatively, the vinyl esters may be prepared conventionally from theacids, by reacting the acid with acetylene, for example. Particularpreference is given—owing to their ready availability—to using vinylesters of saturated aliphatic monocarboxylic acids having 9 to 11 carbonatoms that are branched on the alpha carbon atom.

As component (a5), the reaction product of acrylic acid and/ormethacrylic acid with the glycidyl ester of an alpha-branchedmonocarboxylic acid having from 5 to 18 carbon atoms per molecule isused. Glycidyl esters of highly branched monocarboxylic acids areavailable under the trade name Cardura. The reaction of the acrylic ormethacrylic acid with the glycidyl ester of a carboxylic acid having atertiary alpha carbon atom may take place before, during or after thepolymerization reaction. As component (a5) it is preferred to use thereaction product of acrylic and/or methacrylic acid with the glycidylester of Versatic acid. This glycidyl ester is available commerciallyunder the name Cardura E10.

As component (a6) it is possible to use all ethylenically unsaturatedmonomers that are substantially free from acid groups and arecopolymerizable with (a1), (a2), (a3), (a4), and (a5) but different from(a1), (a2), (a3), and (a4), or mixtures of such monomers (a6) Suitablecomponents (a6) include

olefins such as ethylene, propylene, 1-butene, 1-pentene, 1-hexene,cyclohexene, cyclopentene, norbornene, butadiene, isoprene,cyclopentadiene and/or dicyclopentadiene;

(meth)acrylamides such as (meth)acrylamide, N-methyl-, N,N-dimethyl-,N-ethyl-, N,N-diethyl-, N-propyl-, N,N-dipropyl, N-butyl-, N,N-dibutyl-,N-cyclohexyl- and/or N,N-cyclohexyl-methyl-(meth)acrylamide;

monomers containing epoxide groups, such as the glycidyl ester ofacrylic acid, methacrylic acid, ethacrylic acid, crotonic acid, maleicacid, fumaric acid and/or itaconic acid;

vinylaromatic hydrocarbons, such as styrene, alpha-alkylstyrenes,especially alpha-methyl-styrene, and/or vinyltoluene;

nitriles such as acrylonitrile and/or methacrylo-nitrile;

vinyl compounds such as vinyl chloride, vinyl fluoride, vinylidenedichloride, vinylidene difluoride; N-vinylpyrrolidone; vinyl ethers suchas ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether,n-butyl vinyl ether, isobutyl vinyl ether and/or vinyl cyclohexyl ether;vinyl esters such as vinyl acetate, vinyl propionate, vinyl butyrate,vinyl pivalate and/or the vinyl ester of 2-methyl-2-ethylheptanoic acid;and/or

polysiloxane macromonomers which have a number average molecular weightMn of from 1000 to 40,000, preferably from 2000 to 20,000, withparticular preference from 2500 to 10,000, and in particular from 3000to 7000, and contain on average from 0.5 to 2.5, preferably from 0.5 to1.5, ethylenically unsaturated double bonds per molecule, as describedin DE-A 38 07 571 on pages 5 to 7, in DE-A 37 06 095 in columns 3 to 7,in EP-B-0 358 153 on pages 3 to 6, in U.S. Pat. No. 4,754,014 in columns5 to 9, in DE-A 44 21 823, or in the international patent application WO92/122615 on page 12, line 18 to page 18, line 10, oracryloxysilane-containing vinyl monomers, preparable by reactinghydroxy-functional silanes with epichlorohydrin and then reacting thatreaction product with methacrylic acid and/or hydroxyalkyl esters of(meth)acrylic acid.

It is preferred to use vinylaromatic hydrocarbons.

It is of advantage to use the polysiloxane macromonomers (a6) togetherwith other monomers (a6). In this case the amount of the polysiloxanemacromonomer or macromonomers (a6) for modifying the acrylate copolymers(A1) should be less than 5% by weight, preferably from 0.05 to 2.5% byweight, with particular preference from 0.05 to 0.8% by weight, based ineach case on the overall weight of the monomers used to prepare thecopolymer (A1). The use of such polysiloxane macromonomers leads to animprovement in the slip of the coatings of the invention.

The nature and amount of components (a1) to (a6) is selected such thatthe finely divided solid acrylate copolymer (A1) has the desired OHnumber, acid number, and glass transition temperature. Finely dividedsolid acrylate copolymers (A1) used with particular preference areobtained by polymerizing

(a1) from 20 to 60% by weight, preferably from 30 to 50% by weight, ofcomponent (a1),

(a2) from 10 to 50% by weight, preferably from 15 to 40% by weight, ofcomponent (a2),

(a3) from 1 to 15% by weight, preferably from 1 to 8% by weight, ofcomponent (a3),

(a4) from 0 to 25% by weight, preferably from 5 to 15% by weight, ofcomponent (a4),

(a5) from 0 to 25% by weight, preferably from 5 to 15% by weight, ofcomponent (a5), and

(a6) from 5 to 30% by weight, preferably from 10 to 20% by weight, ofcomponent (a6),

the sum of the weight fractions of components (a1) to (a6) being in eachcase 100% by weight.

The water-soluble or water-dispersible finely divided solid acrylatecopolymers (A) for use in accordance with the invention may be presentindividually or as a mixture.

If they are to be used in a mixture, it should be ensured that finelydivided solid acrylate copolymers (A) containing functional groups (i)are not combined with finely divided solid acrylate copolymers (A)containing functional groups (ii), since this may lead to the formationof insoluble electrolyte complexes.

Furthermore, the finely divided solid acrylate copolymers (A) mayadditionally comprise binders (A) which per se are not dispersible orsoluble in water but which can be dispersed in water in the presence ofthe water-soluble or dispersible acrylate copolymers (A). Examples ofsuitable binders (A) not soluble or dispersible in water come from theoligomer and/or polymer classes described below, with the proviso thatthey contain no hydrophilic functional groups (i), (ii) or (iii) or onlyso few such groups as not to result in water-solubility or-dispersibility.

If, in the preparation of the coating compositions of the invention, themixing of the components (I), (II), (III), and (IV) is to take place bymanual stirring, it is of advantage for the coating composition of theinvention if the finely divided solid acrylate copolymers (A) areselected such that their 50% strength solution in ethoxyethyl propionateat 23° C. has a viscosity of ≦10 dPas. Where mechanical mixing is totake place, it is possible to use binders (A) of higher viscosity, whose50% strength solution in ethoxyethyl propionate at 23° C has a viscosityof ≦100 dpas. The viscosity is limited at the top end only by theperformance capacity of the mixing equipment.

The particle size of the finely divided solid acrylate copolymers (A) isnot critical. What is important is that the particle size is not made sosmall that the particles tend to agglomerate and/or become respirable,or so large that redissolution or redispersion is hindered or prevented.In accordance with the invention, particle sizes of from 5 to 500 μm areof advantage.

The preparation of the finely divided solid acrylate copolymers (A) hasno special features in terms of its method but instead takes place inaccordance with, the customary and known methods of polymerization inbulk, solution or emulsion or by suspension polymerization orprecipitation polymerization and drying of the resulting acrylatecopolymers (A) with the aid of customary and known methods and apparatusand under conditions which ensure the formation of finely divided solidproducts. Examples of suitable drying methods are spray drying, freezedrying, and precipitation from solution, emulsion or suspension.

In many cases it is of advantage, after preparing the acrylatecopolymers (A), to add to them aqueous media, which may include at leastone of the neutralizing agents (D) described below, in order to convertthem into a secondary dispersion, which is then dried.

In the case of polymerization in solution, solvents are used which donot pose a hindrance to drying but are instead easy to remove from theacrylate copolymers (A). It is preferred to use solvents having acomparatively high vapor pressure. The same applies to the cosolventswhich may be used in the emulsion, suspension or precipitationpolymerization or for preparing the secondary dispersions, or to thenonsolvents which are used for precipitation.

For the preparation of the acrylate copolymers (A1) used with preferencein accordance with the invention it is advantageous to usepolymerization initiators.

Examples of suitable polymerization initiators are initiators which formfree radicals, such as tert-butyl peroxyethylhexanoate, benzoylperoxide, di-tert-amyl peroxide, azobisisobutyronitrile, and tert-butylper-benzoate, for example. The initiators are used preferably in anamount from 1 to 25% by weight, with particular preference from 2 to 10%by weight, based on the overall weight of the monomers.

The polymerization is appropriately conducted at a temperature from 80to 200° C., preferably from 110 to 180C. Preferred solvents used areethoxyethyl propionate and isopropoxypropanol.

The acrylate copolymer (A1) is preferably prepared by a two-stageprocess, since in that way the resultant coating compositions of theinvention possess better processing properties. It is thereforepreferred to use acrylate copolymers (A1) which are obtainable by

1. polymerizing a mixture of (a1), (a2), (a4), (a5), and (a6), or amixture of portions of components (a1), (a2), (a4), (a5), and (a6), inan organic solvent and/or in one of the reactive diluents mentionedbelow,

2. after at least 60% by weight of the mixture consisting of (a1), (a2),(a4), (a5), and, where used, (a6) have been added, adding (a3) and anyremainder of components (a1), (a2), (a4), (a5), and (a6), and continuingpolymerization, and

3. after the end of the polmerization, subjecting the resultingpolyacrylate resin if desired to at least partial neutralization, i.e.,converting the acid groups into the corresponding acid anion groups.

In addition, however, it is also possible to include components (a4)and/or (a5) in the initial charge together with at least part of thesolvent, and to meter in the remaining components. Moreover, it is alsopossible for components (a4) and/or (a5) to be included only in part inthe initial charge, together with at least part of the solvent, and forthe remainder of these components to be added as described above.Preferably, for example, at least 20% by weight of the solvent and about10% by weight of component (a4) and (a5), and also, if desired, portionsof components (a1) and (a6), are included in the initial charge.

Preference is also given to preparing the acrylate copolymers (A1) bymeans of a two-stage process whose first stage lasts from 1 to 8 hours,preferably from 1.5 to 4 hours, and in which a mixture of (a3) and anyremainder of components (a1), (a2), (a4), (a5), and (a6) is added overthe course of from 20 to 120 minutes, preferably over the course of from30 to 90 minutes. Following the end of the addition of the mixture of(a3) and any remainder of components (a1), (a2), (a4), (a5), and (a6),polymerization is continued until all of the monomers used haveundergone substantially complete reaction. The second stage in thisprocess may immediately follow the first. Alternatively, the secondstage may be commenced after a certain time, for example after from 10minutes to 10 hours.

The amount and rate of addition of the initiator are preferably chosenso as to give a polyacrylate resin (A1) having a number averagemolecular weight Mn of from 1000 to 30,000 daltons. It is preferred tocommence the initiator feed at a certain time, generally about 15minutes, before the feeding of the monomers. Preference is given,further, to a process in which the addition of initiator is commenced atthe same point in time as the addition of the monomers and is endedabout half an hour after the addition of the monomers has ended. Theinitiator is preferably added in a constant amount per unit time.Following the end of the addition of initiator, the reaction mixture isheld at polymerization temperature until (generally 1.5 hours) all ofthe monomers used have undergone substantially complete reaction.“Substantially complete reaction” is intended to denote that preferably100% by weight of the monomers used have undergone reaction but that itis also possible for a small residual monomer content of not more thanup to about 0.5% by weight, based on the weight of the reaction mixture,to remain unreacted.

Preferably, the monomers for preparing the acrylate copolymers (A1) arepolymerized at a polymerization solids which is not too high, preferablyat a polymerization solids of from 80 to 50% by weight, based on thecomonomers, and then the solvents are removed in part by distillation,so that the resulting acrylate copolymer solutions (A1) have a solidscontent of preferably from 100 to 60% by weight.

The preparation of the finely divided solid acrylate copolymers (A1),especially the finely divided solid acrylate copolymers (A1) for use inaccordance with the invention takes place by means of the methods ofcontinuous or batchwise copolymerization that are known and customary inthe polymers field, under atmospheric pressure or superatmosphericpressure, in stirred tanks, autoclaves, tube reactors or Taylorreactors.

Examples of suitable (co)polymerization processes for preparing theacrylate copolymers (A1) are described in the patents DE-A-197 09 465,DE-C-197 09 476, DE-A-28 48 906, DE-A-195 24 182, EP-A-0 554 783, WO95/27742 or WO 82/02387.

Taylor reactors are advantageous.

Taylor reactors, which serve to convert substances under the conditionsof Taylor flow, are known. They consist substantially of two coaxialconcentric cylinders of which the outer is fixed and the inner rotates.The reaction space is the volume formed by the gap between thecylinders. Increasing angular velocity ω_(i) of the inner cylinder isaccompanied by a series of different flow patterns which arecharacterized by a dimensionless parameter, known as the Taylor numberTa. In addition to the angular velocity of the stirrer, the Taylornumber is also dependent on the kinematic viscosity v of the fluid inthe gap and on the geometric parameters, the external radius of theinner cylinder r_(i), the internal radius of the outer cylinder r_(o),and the gap width d, the difference between the two radii, in accordancewith the following formula:

Ta=ω _(i) r _(i) d v ⁻¹(d/r _(i))^(½)  (I)

where d=r_(o)−r_(i).

At low angular velocity, the laminar Couette flow, a simple shear flow,develops. If the rotary speed of the inner cylinder is increasedfurther, then, above a critical level, alternately contrarotatingvortices (rotating in opposition) occur, with axes along the peripheraldirection. These vortices, called Taylor vortices, are rotationallysymmetric and have a diameter which is approximately the same size asthe gap width. Two adjacent vortices form a vortex pair or vortex cell.

The basis for this behavior is the fact that, in the course of rotationof the inner cylinder with the outer cylinder at rest, the fluidparticles that are near to the inner cylinder are subject to a greatercentrifugal force than those at a greater distance from the innercylinder. This difference in the acting centrifugal forces displaces thefluid particles from the inner to the outer cylinder. The centrifugalforce acts counter to the viscosity force, since for the motion of thefluid particles it is necessary to overcome the friction. Any increasein the rotary speed is accompanied by an increase in the centrifugalforce as well. The Taylor vortices are formed when the centrifugal forceexceeds the stabilizing viscosity force.

In the case of Taylor flow with a low axial flow, each vortex pairpasses through the gap, with only a low level of mass transfer betweenadjacent vortex pairs. Mixing within such vortex pairs is very high,whereas axial mixing beyond the pair boundaries is very low. A vortexpair may therefore be regarded as a stirred tank in which there isthorough mixing. Accordingly, the flow system behaves as an ideal flowtube in that the vortex pairs pass through the gap with constantresidence time, like ideal stirred tanks.

Of advantage in accordance with the invention here are Taylor reactorshaving an external reactor wall located within which there is aconcentrically or eccentrically disposed rotor, a reactor floor, and areactor lid, which together define the annular reactor volume, at leastone means for metered addition of reactants, and a means for thedischarge of product, where the reactor wall and/or the rotor are or isgeometrically designed in such a way that the conditions for Taylor floware met over substantially the entire reactor length in the reactorvolume, i.e., in such a way that the annular gap broadens in thedirection of flow traversal.

The further essential constituent of the coating compositions of theinvention is component (I). It comprises at least one binder (A)containing functional groups which react with isocyanate groups.Suitable functional groups are all those described above in connectionwith component (IV).

Examples of suitable binders (A) are linear and/or branched and/orblock, comb and/or random poly(meth)acrylates or acrylate copolymers,polyesters, alkyds, polyurethanes, acrylated polyurethanes, acrylatedpolyesters, poly-lactones, polycarbonates, polyethers, epoxy resin-amineadducts, (meth)-acrylatediols, partially saponified polyvinyl esters orpolyureas, of which the acrylate copolymers, the polyesters, thepolyurethanes, the polyethers, and the epoxy resin-amine adducts areparticularly advantageous and are therefore used with particularpreference.

Regarding the preparability, the handling and the particularlyadvantageous properties of the coating compositions of the inventionthat are prepared using them, the acrylate copolymers, the polyestersand/or the polyurethanes, but in particular the acrylate copolymers,afford very particular advantages, and so are used with very particularpreference in accordance with the invention.

Where binders (A) which per se are not water-soluble orwater-dispersible are used in component (I), it should be ensured that,by way of component (III) and/or (IV), the amount of water-soluble orwater-dispersible binders (A) introduced into the coating composition ofthe invention is sufficient for the binders (A) overall to form a stabledispersion.

In component (I) as well, particular preference is given to using theabove-described acrylate copolymers (A1) and also the polyester resins(A2) and/or polyurethane resins (A3) described below.

It is very particularly preferred to use the acrylate copolymers (A1)which have been prepared in what are known as reactive diluents assolvents, which are not separated off after the copolymerization. Thesereactive diluents participate in the reaction with the crosslinkingcomponent (II).

Examples of suitable thermally crosslinkable reactive diluents arebranched, cyclic and/or acyclic C₉-C₁₆ alkanes functionalized with atleast two hydroxyl groups, preferably dialkyloctanediols, especially thepositionally isomeric diethyloctanediols.

Further examples of suitable thermally crosslinkable reactive diluentsare oligomeric polyols obtainable by hydroformylation and subsequenthydrogenation of oligomeric intermediates themselves obtained bymetathesis reactions of acyclic monoolefins and cyclic monoolefins;examples of suitable cyclic monoolefins are cyclobutene, cyclopentene,cyclohexene, cyclooctene, cycloheptene, norbornene, and 7-oxanorbornene;examples of suitable acyclic monoolefins are contained in hydrocarbonmixtures obtained in petroleum processing by cracking (C₅ cut); examplesof suitable oligomeric polyols for use in accordance with the inventionhave a hydroxyl number (OHN) of from 200 to 450, a number averagemolecular weight Mn of from 400 to 1000, and a mass average molecularweight Mw of from 600 to 1100.

Further examples of suitable thermally crosslinkable reactive diluentsare hyperbranched compounds having a tetrafunctional central group,derived from ditrimethylolpropane, diglycerol, ditrimethylolethane,pentaerythritol, tetrakis(2-hydroxyethyl)methane,tetrakis(3-hydroxypropyl)methane or 2,2-bishydroxy-methyl-1,4-butanediol(homopentaerythritol). These reactive diluents may be prepared by thecustomary and known methods of preparing hyperbranched and dendrimericcompounds. Suitable synthesis methods are described, for example, in thepatents WO 93/17060 and WO 96/12754 or in the book by G. R. Newkome, C.N. Moorefield and F. Vögtle, “Dendritic Molecules, Concepts, Syntheses,Perspectives”, VCH, Weinheim, N.Y., 1996.

Further examples of suitable reactive diluents are polycarbonatediols,polyesterpolyols, poly(meth)-acrylatediols or hydroxy-containingpolyaddition products.

Examples of suitable isocyanate-reactive solvents are butyl glycol,2-methoxypropanol, -n-butanol, methoxy-butanol, n-propanol, ethyleneglycol monomethyl ether, ethylene glycol monoethyl ether, ethyleneglycol monobutyl ether, diethylene glycol monomethyl ether, diethyleneglycol monoethyl ether, diethylene glycol diethylene ether, diethyleneglycol monobutyl ether, trimethylolpropane, ethyl 2-hydroxypropionate or3-methyl-3-methoxybutanol and also derivatives based on propyleneglycol, e.g., ethoxyethyl propionate, isopropoxypropanol ormethoxypropyl acetate.

Said reactive diluents, especially the functionalized alkanes, and/orthe isocyanate-reactive solvents may also be present in component (III).

Suitable polyester resins (A2) include all polyesters having theabove-indicated OH numbers, acid numbers, molecular weights, andviscosities.

Use is made in particular of polyester resins (A2) obtainable byreacting

p1), optionally sulfonated polycarboxylic acids or their esterifiablederivatives, together if desired with monocarboxylic acids,

p2) polyols, together if desired with monools,

p3) if desired, further, modifying components, and

p4) if desired, a component which is reactive with the reaction productof (p1), (p2) and, where used, (p3).

Examples that may be given of polycarboxylic acids that may be used ascomponent (p1) are aromatic, aliphatic, and cycloaliphaticpolycarboxylic acids. As component (p1) it is preferred to use aromaticand/or aliphatic polycarboxylic acids.

Examples of suitable polycarboxylic acids are phthalic acid, isophthalicacid, terephthalic acid, phthalic, isophthalic or terephthalicmonosulfonate, halophthalic acids, such as tetrachlorophthalic ortetrabromophthalic acid, adipic acid, glutaric acid, azelaic acid,sebacic acid, fumaric acid, maleic acid, trimellitic acid, pyromelliticacid, tetrahydrophthalic acid, hexahydrophthalic acid,1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid,1,4-cyclohexanedicarboxylic acid, 4-methylhexahydrophthalic acid,endomethylenetetrahydrophthalic acid, tricyclodecanedicarboxylic acid,endoethylenehexahydrophthalic acid, camphoric acid,cyclohexanetetracarboxylic acid, or cyclobutanetetracarboxylic acid. Thecycloaliphatic polycarboxylic acids may be used either in their cis orin their trans form or as a mixture of both forms. Also suitable are theesterifiable derivatives of the aforementioned polycarboxylic acids,such as their monoesters or polyesters with aliphatic alcohols havingfrom 1 to 4 carbon atoms or hydroxy alcohols having from 1 to 4 carbonatoms, for example. It is also possible to use the anhydrides of theabovementioned acids, where they exist.

If desired, together with the polycarboxylic acids it is also possibleto use monocarboxylic acids, such as benzoic acid, tert-butylbenzoicacid, lauric acid, isononanoic acid, and fatty acids of naturallyoccurring oils, for example. Isononanoic acid is a preferredmonocarboxylic acid used.

Suitable alcohol components (p2) for preparing the polyester (A2) arepolyhydric alcohols, such as ethylene glycol, propanediols, butanediols,hexanediols, neopentyl hydroxypivalate, neopentyl glycol, diethyleneglycol, cyclohexanediol, cyclohexanedimethanol, trimethylpentanediol,ethylbutylpropanediol, ditrimethylolpropane, trimethylolethane,trimethylolpropane, glycerol, pentaerythritol, dipentaerythritol,trishydroxyethyl isocyanate, polyethylene glycol, polypropylene glycol,alone or together with monohydric alcohols, such as butanol, octanol,lauryl alcohol, cyclohexanol, tert-butylcyclohexanol, ethoxylated and/orpropoxylated phenols, for example.

Compounds suitable as component (p3) for preparing the polyesters (A2)include in particular those having a group which is reactive toward thefunctional groups of the polyester, with the exception of the compoundsspecified as component (p4). As modifying component (p3) it is preferredto use polyisocyanates and/or diepoxide compounds, and also, if desired,monoisocyanates and/or monoepoxide compounds. Suitable components (p3)are described, for example, in DE-A-40 24 204 on page 4, lines 4 to 9.

Compounds suitable as component (p4) for preparing the polyesters (A2)are those compounds which in addition to a group that is reactive towardthe functional groups of the polyester (A2) also contain a tertiaryamino group, examples including monoisocyanates containing at least onetertiary amino group, or mercapto compounds containing at least onetertiary amino group. For details, refer to DE-A-40 24 204, page 4,lines 10 to 49.

The polyester resins (A2) are prepared in accordance with the knownmethods of esterification, as is described, for example, in DE-A-40 24204, page 4, lines 50 to 65. This reaction takes place usually attemperatures between 180 and 280° C., in the absence or presence of anappropriate esterification catalyst, such as lithium octoate, dibutyltinoxide, dibutyltin dilaurate or para-toluenesulfonic acid, for example.

The polyester resins (A2) are normally prepared in the presence of smallamounts of an appropriate solvent as entrainer. Examples of entrainersused include aromatic hydrocarbons, such as xylene in particular, and(cyclo aliphatic hydrocarbons, e.g. cyclohexane or methylcyclohexane.

It is particularly preferred to use polyester resins (A2) which havebeen prepared by a two-stage process, by first preparing ahydroxyl-containing polyester having an OH number of from 100 to 300 mgKOH/g, an acid number of less than 10 mg KOH/g, and a number averagemolecular weight Mn of from 500 to 2000 daltons, which is then reactedin a second stage with carboxylic anhydrides to give the desiredpolyester resin (A2). The amount of carboxylic anhydrides in this caseis chosen so that the resulting polyester resin (A2) has the desiredacid number. Acid anhydrides suitable for this reaction are all thosecommonly used, such as hexahydrophthalic anhydride, trimelliticanhydride, pyromellitic anhydride, phthalic anhydride, camphoricanhydride, tetrahydrophthalic anhydride, succinic anhydride, andmixtures of these and/or other anhydrides, and especially anhydrides ofaromatic polycarboxylic acids, such as trimellitic anhydride, forexample.

It is possible if desired for the acrylate copolymer (A1) to have beenprepared at least in part in the presence of the polyester resin (A2).In this case, advantageously at least 20% by weight and with particularadvantage from 40 to 80% by weight of the acrylate copolymer (A1) areprepared in the presence of the polyester resin (A2). Any remainder ofthe acrylate copolymer (A1) is added subsequently to the component (I).In this case it is possible for this already polymerized resin to havethe same monomer composition as the acrylate copolymer (A1) synthesizedin the presence of the polyester resin (A2). Alternatively, ahydroxyl-containing acrylate copolymer (A1) having a different monomercomposition may be added. Also possible is the addition of a mixture ofdifferent acrylate copolymers (A1) and/or polyester resins (A2) withpossibly one resin having the same monomer composition as the acrylatecopolymer (A1) synthesized in the presence of the polyester resin (A2).

As the polyurethane resin (A3) for use in accordance with the invention,containing hydroxyl and acid groups, suitable resins include allpolyurethane resins having the indicated OH numbers, acid numbers,molecular weights, and viscosities.

Suitable polyurethane resins (A3) are described, for example, in thefollowing documents: EP-A-355 433, DE-A-35 45 618, DE-A-38 13 866,DE-A-32 10 051, DE-A-26 24 442, DE-A-37 39 332, U.S. Pat. No. 4,719,132,EP-A-0 089 497, U.S. Pat. No. 4,558,090, U.S. Pat. No. 4,489,135,DE-A-36 28 124, EP-A-0 158 099, DE-A-29 26 584, EP-A-0 195 931, DE-A-3321 180 and DE-A-40 05 961.

In component (I) it is preferred t o us e polyurethane resins (A3) whichare preparable by reacting isocyanato-containing prepolymers withcompounds that are reactive toward isocyanate groups.

The preparation of isocyanato-containing prepolymers may take place byreacting polyols having a hydroxyl number of from 10 to 1800, preferablyfrom 50 to 1200 mg KOH/g, with excess polyisocyanates at temperatures ofup to 150° C., preferably from 50 to 130° C., in organic solvents whichare unable to react with isocyanates. The equivalence ratio of NCO to OHgroups is situated between 2.0:1.0 and >1.0:1.0, preferably between1.4:1 and 1.1:1.

The polyols used to prepare the prepolymer may be of low molecularweight and/or high molecular weight and may contain groups that are slowto react and are anionic or capable of forming anions. It is alsopossible to use low molecular weight polyols having a molecular weightof from 60 up to 400 daltons to prepare the isocyanato-containingprepolymers. In this case amounts of up to 30% by weight of the overallpolyol constituents are used, preferably from about 2 to 20% by weight.

In order to obtain an NCO prepolymer of high flexibility, a highfraction of a predominantly linear polyol having a preferred OH numberof from 30 to 150 mg KOH/g should be added. Up to 97% by weight of theoverall polyol may consist of saturated and unsaturated polyestersand/or polyethers having a number average molecular weight Mn of from400 to 5000 daltons. The selected polyetherdiols should not introduceexcessive amounts of ether groups, since otherwise the polymers formedstart to swell in water. Polyesterdiols are prepared by esterifyingorganic dicarboxylic acids or their anhydrides with organic diols, orderive from a hydroxycarboxylic acid or from a lactone. In order toprepare branched polyester polyols, it is possible to employ a minorproportion of polyols or polycarboxylic acids having a higherfunctionality.

The alcohol component used to prepare the polyurethane resins preferablyconsists at least to a certain extent of

u₁) at least one diol of the formula (I′)

 in which R₁ and R₂ are each an identical or different radical and arean alkyl radical having from 1 to 18 carbon atoms, an aryl radical or acycloaliphatic radical, with the proviso that R₁ and/or R₂ must not bemethyl, and/or

u₂) at least one diol of the formula (II′)

 in which R₃, R₄, R₆ and R₇ are each identical or different radicals andare an alkyl radical having from 1 to 6 carbon atoms, a cycloalkylradical or an aryl radical and R₅ is an alkyl radical having from 1 to 6carbon atoms, an aryl radical or an unsaturated alkyl radical havingfrom 1 to 6 carbon atoms, and n is either 0 or 1.

Suitable diols (u₁) are all propanediols of the formula (I′) in whicheither R₁ or R₂ or R₁ and R₂ is or are other than methyl, such as2-butyl-2-ethyl-1,3-propanediol, 2-butyl-2-methyl-1,3-propanediol,2-phenyl-2-methyl-1,3-propanediol, 2-propyl-2-ethyl-1,3-propanediol,2-di-tert-butyl-1,3-propanediol, 2-butyl-2-propyl-1,3-propanediol,1-dihydroxymetbylbicyclo-[2.2.]heptane, 2,2-diethyl-1,3-propanediol,2,2-dipropyl-1,3-propanediol, 2-cyclohexyl-2-methyl-1,3-propanediol, etcetera, for example.

Examples of diols (u₂) (formula (II′)) that may be used include2,5-dimethyl-2,5-hexanediol, 2,5-diethyl-2,5-hexanediol,2-ethyl-5-methyl-2,5-hexanediol, 2,4-dimethyl-2,4-pentanediol,2,3-dimethyl-2,3-butanediol, 1,4-bis(2′-hydroxypropyl)benzene, and1,3-bis(2′-hydroxypropyl)benzene.

As diols (u₁) it is preferred to use 2-propyl-2-ethyl-1,3-propanediol,2,2-diethyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, and2-phenyl-2-ethyl-1,3-propanediol, and as component (u₂) it is preferredto use 2,3-dimethyl-2,3-butanediol and also 2,5-dimethyl-2,5-hexanediol.Particular preference is given to using 2-butyl-2-ethyl-1,3-propanedioland also 2-phenyl-2-ethyl-1,3-propanediol as component (u₁) and2,5-dimethyl-2,5-hexanediol as component (u₂).

The diols (u₁) and/or (u₂) are commonly used in an amount of from 0.5 to15% by weight, preferably from 1 to 7% by weight, based in each case onthe overall weight of the synthesis components used to prepare thepolyurethane resins (A3).

Typical multifunctional isocyanates used to prepare the polyurethaneresins (A3) are aliphatic, cycloaliphatic and/or aromaticpolyisocyanates containing at least two isocyanate groups per molecule.Preference is given to the isomers or isomer mixtures of organicdiisocyanates. Owing to their good stability to ultraviolet light,(cyclo)aliphatic diisocyanates give rise to products having a lowtendency to yellow. The polyisocyanate component used to form theprepolymer may also contain a fraction of polyisocyanates of higherfunctionality, provided that no gelling is caused as a result. Productswhich have become established as triisocyanates are those formed bytrimerization or oligomerization of diisocyanates or by reaction ofdiisocyanates with polyfunctional compounds containing OH or NH groups.The average functionality may be lowered if desired by addingmonoisocyanates.

Examples of polyisocyanates that may be used include phenylenediisocyanate, tolylene diisocyanate, xylylene diisocyanate, bisphenylenediisocyanate, naphthylene diisocyanate, diphenylmethane diisocyanate,isophorone diisocyanate, cyclobutane diisocyanate, cyclopentylenediisocyanate, cyclohexylene diisocyanate, methylcyclohexylenediisocyanate, dicyclohexylmethane diisocyanate, ethylene diisocyanate,trimethylene diisocyanate, tetramethylene diisocyanate, pentamethylenediisocyanate, hexamethylene diisocyanate, propylene diisocyanate,ethylethylene diisocyanate, and trimethylhexane diisocyanate.

To prepare high-solids polyurethane solutions (A3), use is made inparticular of diisocyanates of the general formula (III′)

where x is a divalent aromatic hydrocarbon radical, preferably anunsubstituted or halogen-, methyl- or methoxy-substituted naphthylene,diphenylene or 1,2-, 1,3- or 1,4-phenylene radical, with particularpreference a 1,3-phenylene radical and R₁ and R₂ are an alkyl radicalhaving 1-4 carbon atoms, preferably a methyl radical. Diisocyanates ofthe formula (III′) are known (their preparation is described, forexample, in EP-A-101 832, U.S. Pat. No. 3,290,350, U.S. Pat. No.4,130,577, and U.S. Pat. No. 4,439,616) and some are availablecommercially (1,3-bis(2-isocyanatoprop-2-yl)benzene, for example, issold by the American Cyanamid company under the tradename TMXDI(META)®).

Further preferred as polyisocyanate components are diisocyanates of theformula (IV′):

where:

R is a divalent alkyl or aralkyl radical having from 3 to 20 carbonatoms and R′ is a divalent alkyl or aralkyl radical having from 1 to 20carbon atoms;

especially 1-isocyanato-2-(3-isocyanatoprop-1-yl)cyclohexane.

Polyurethanes are generally incompatible with water unless specificconstituents are incorporated and/or special preparation steps taken inthe course of their synthesis. To prepare the polyurethane resins (A3)it is thus possible to use compounds which contain two H-active groupsthat are reactive with isocyanate groups, and at least one group whichensures dispersibility in water. Suitable groups of this kind arenonionic groups (e.g., polyethers), anionic groups, mixtures of thesetwo groups, or cationic groups.

Accordingly it is possible to build into the polyurethane resin (A3) anacid number which is sufficiently large that the neutralized product canbe dispersed safely in water. For this purpose use is made of compoundscontaining at least one isocyanate-reactive group and at least one groupcapable of forming anions. Suitable isocyanate-reactive groups are, inparticular, hydroxyl groups and also primary and/or secondary aminogroups. Groups capable of forming anions are carboxyl, sulfonic acidand/or phosphonic acid groups. It is preferred to use alkanoic acidshaving two substituents on the alpha carbon atom.

The substituent may be a hydroxyl group, an alkyl group or an alkylolgroup. These polyols have at least one, generally from 1 to 3, carboxylgroups in the molecule. They have from 2 to about 25, preferably from 3to 10 carbon atoms. The carboxyl-containing polyol may account for from3 to 100% by weight, preferably from 5 to 50% by weight, of the overallpolyol constituent in the NCO prepolymer.

The amount of ionizable carboxyl groups that is available by virtue ofthe carboxyl group neutralization in salt form is generally at least0.4% by weight, preferably at least 0.7% by weight, based on the solids.The upper limit is approximately 12% by weight. The amount ofdihydroxyalkanoic acids in the unneutralized prepolymer gives an acidnumber of at least 5 mg KOH/g, preferably at least 10 mg KOH/g. Withvery low acid numbers, it is generally necessary to take furthermeasures to achieve dispersibility in water. The upper limit on the acidnumber is 150 mg KOH/g, preferably 40 mg KOH/g, based on the solids. Theacid number is preferably situated within the range from 20 to 40 mgKOH/g.

The isocyanate groups of the isocyanato-containing prepolymer arereacted with a modifier. The modifier is preferably added in an amountsuch that instances of chain extension and thus of molecular weightincrease occur. Modifiers used are preferably organic compoundscontaining hydroxyl and/or secondary and/or primary amino groups,especially polyols with a functionality of two, three and/or more.Examples of polyols which can be used include trimethylolpropane,1,3,4-butanetriol, glycerol, erythritol, mesoerythritol, arabitol,adonitol, etc. Trimethylolpropane is used with preference.

To prepare the polyurethane resin (A3) it is preferred first to preparean isocyanato-containing prepolymer from which the desired polyurethaneresin (A3) is then prepared by further reaction, preferably chainextension. The reaction of the components takes place in accordance withthe well-known processes of organic chemistry (cf., e.g.,Kunststoff-Handbuch, Volume 7: Polyurethane, edited by Dr. Y. Oertel,Carl Hanser Verlag, Munich, Vienna, 1983). Examples of the preparationof the prepolymers are described in DE-A 26 24 442 and DE-A 32 10 051.The polyurethane resins (A3) may be prepared by the known methods (e.g.,acetone method).

The components are preferably reacted in ethoxyethyl propionate (EEP) assolvent. The amount of EEP in this case may be variable within widelimits and should be sufficient for the formation of a prepolymersolution of appropriate viscosity. In general up to 70% by weight,preferably from 5 to 50% by weight, and with particular preference lessthan 20% by weight of solvent is used, based on the solids. Accordingly,the reaction may be carried out with very particular preference forexample, at a solvent content of 10-15% by weight EEP, based on thesolids.

The reaction of the components may take place if desired in the presenceof a catalyst, such as organotin compounds and/or tertiary amines.

To prepare the prepolymers, the amounts of the components are chosensuch that the equivalents ratio of NCO groups to OH groups is situatedbetween 2.0:1.0 and >1.0:1.0, preferably between 1.4:1 and 1.1:1.

The NCO prepolymer contains at least about 0.5% by weight of isocyanategroups, preferably at least 1% by weight of NCO, based on the solids.The upper limit is approximately 15% by weight, preferably 10% byweight, with particular preference 5% by weight of NCO.

In particular, the especially preferred component (I) comprises asbinder (A)

(A1) at least 20% by weight of at least one acrylate copolymer (A1),

(A2) from 0 to 30% by weight of at least one polyester resin (A2),

(A3) from 0 to 80% by weight of at least one polyurethane resin (A3),and

(A4) from 0 to 10% by weight of at least one further binder (A),

the sum of the weight fractions of components (A1) to (A4) being in eachcase 100% by weight.

Besides the binders (A), the component (I) may include as constituent(B) all customary coatings pigments and/or fillers in fractions of from0 to 60% by weight, based on component (I). In this context it ispossible to use not only the pigments that are common in aqueous coatingcompositions and which do not react with water and/or do not dissolve inwater, but also the pigments commonly employed in conventional coatingcompositions. The pigments may comprise organic or inorganic compoundsand may impart color and/or effect. The coating composition of theinvention therefore ensures, owing to this large number of appropriatepigments, a universal scope for use, and permits the realization of alarge number of shades.

As effect pigments it is possible to use metal flake pigments, such ascommercially customary aluminum bronzes, aluminum bronzes chromated inaccordance with DE-A-36 36 183, and commercially customary stainlesssteel bronzes, and also nonmetallic effect pigments, such as pearlescentpigments and interference pigments for example. Examples of suitableinorganic color pigments are titanium dioxide, iron oxides, Sicotransyellow, and carbon black. Examples of suitable organic color pigmentsare indanthrene blue, Cromophthal red, Irgazine orange and Heliogengreen. Examples of suitable fillers are chalk, calcium sulfates, bariumsulfate, silicates such as talc or kaolin, silicas, oxides such asaluminum hydroxide or magnesium hydroxide, nanoparticles or organicfillers such as textile fibers, cellulose fibers, polyethylene fibers orwood flour.

As a further constituent (C) the component (I) may include at least oneorganic solvent which can be diluted with water. Such solvents may alsoparticipate in the reaction with the crosslinking component (II) and maytherefore act as reactive diluents. Examples of suitable solvents orreactive diluents are those specified above.

Also suitable as solvents are esters, ketones, keto esters, glycolethers such as ethylene, propylene or butylene glycol ethers, glycolesters such as ethylene, propylene or butylene glycol esters, or glycolether esters such as ethoxyethyl propionate and isopropoxypropanol.Further suitable solvents include aliphatic and aromatic solvents suchas dipentene, xylene or Shellsol®.

As constituent (D) the component (I) comprises, if desired, at least oneneutralizing agent.

Examples of suitable neutralizing agents for functional groups (i) whichcan be converted into cations are organic and inorganic acids such assulfuric acid, hydrochloric acid, phosphoric acid, formic acid, aceticacid, lactic acid, dimethylolpropionic acid or citric acid.

Examples of suitable neutralizing agents for functional groups (ii)which can be converted into anions are ammonia, ammonium salts, such asammonium carbonate or ammonium hydrogen carbonate, for example, and alsoamines, such as trimethylamine, triethylamine, tributylamine,dimethylaniline, diethylaniline, triphenylamine, dimethylethanolamine,diethylethanolamine, methyldiethanolamine, triehlianolamine, and thelike. Neutralization may be effected in organic phase or in aqueousphase. Dimethylethanolamine is a preferred neutralizing agent used.

The amount of neutralizing agent (D) used in total in the coatingcomposition of the invention is chosen such that from 1 to 100equivalents, preferably from 50 to 90 equivalents, of the functionalgroups (i) or (ii) of the binder (A) are neutralized. The neutralizingagent (D) may be added to component (I), (II) and/or (III) or during thepreparation of component (IV) before it is dried. Preferably, however,the neutralizing agent (D) is added to component (III).

As constituent (E) the component (I) may comprise at least one rheologycontrol additive. Examples of suitable rheology control additives arethose known from the patents WO 94/22968, EP-A-0 276 501, EP-A-0 249201, and WO 97/12945; crosslinked polymeric microparticles, as disclosedfor example in EP-A-0 008 127; inorganic phyllosilicates such asaluminum magnesium silicates, sodium magnesium phyllosilicates, andsodium magnesium fluorine lithium phyllosilicates of the montmorillonitetype; silicas such as Aerosils; or synthetic polymers containing ionicand/or associative groups, such as polyvinyl alcohol,poly(meth)acrylamide, poly(meth)acrylic acid, polyvinylpyrrolidone,styrene-maleic anhydride or ethylene maleic anhydride copolymers andtheir derivatives, or hydrophobically modified ethoxylated urethanes orpolyacrylates. Preferred rheology control additives used arepolyurethanes.

The component (I) may further comprise at least one additional customarycoatings additive (E). Examples of such additives are defoamers,dispersing auxiliaries, emulsifiers, and leveling agents.

Of course, said additives (E) may also be added separately to thecoating composition. In this case the additives (E) are then referred toas component (V).

To prepare the coating compositions of the invention it is preferred touse components (I) which consist of

from 20 to 90% by weight, preferably from 35 to 80% by weight, of thebinder (A), especially the polymeric or oligomeric resins (A1), (A2),(A3), and/or (A4),

from 0 to 60% by weight of at least one pigment and/or filler (B),

from 0 to 50% by weight, preferably from 10 to 40% by weight, of atleast one organic, optionally water-dilutable solvent and/or reactivediluent

from 0 to 20% by weight, preferably from 0.1 to 10% by weight, of atleast one neutralizing agent (D), and

from 0 to 20% by weight, preferably from 2 to 10% by weight, of at leastone customary auxiliary and/or additive (coatings additive) (E),

the sum of the weight fractions of all the constituents being in eachcase 100% by weight.

The further key constituent of the coating composition of the inventionis at least one crosslinking agent (F), which is present in component(II).

The crosslinking agents (F) comprise at least one diisocyanate and/orpolyisocyanate (F) which if desired is dispersed or dissolved in one ormore organic, optionally water-dilutable solvents.

The polyisocyanate component (F) comprises organic polyisocyanates,especially those known as paint polyisocyanates, containing freeisocyanate groups attached to aliphatic, cycloaliphatic, araliphaticand/or aromatic moieties. Preference is given to using polyisocyanatescontaining from 2 to 5 isocyanate groups per molecule and havingviscosities of from 100 to 10,000, preferably from 100 to 5000, and,where manual mixing of the components (I), (II) and (III) isenvisaged—in particular from 5000 to 2000 mPas (at 23° C.). If desired,small amounts of organic solvent (G) may be added to thepolyisocyanates, preferably from 1 to 25% by weight based on straightpolyisocyanate, in order thus to improve the ease of incorporation ofthe isocyanate and, where appropriate, to lower the viscosity of thepolyisocyanate to a level within the aforementioned ranges. Examples ofsuitable solvent additives for (G) the polyisocyanates are ethoxyethylpropionate, amyl methyl ketone, and butyl acetate. Furthermore, thepolyisocyanates may have been conventionally hydrophilically orhydrophobically modified.

Examples of suitable isocyanates are described by way of example in“Methoden der organischen Chemie”, Houben-Weyl, Volume 14/2, 4thEdition, Georg Thieme Verlag, Stuttgart 1963, pages 61 to 70, and by W.Siefken, Liebigs Annalen der Chemie, Volume 562, pages 75 to 136.Suitable examples include the isocyanates specified in the descriptionof the polyurethane resins (A3), and/or isocyanato-containingpolyurethane prepolymers which may be prepared by reacting polyols withan excess of polyisocyanates and which are preferably of low viscosity.

Further examples of suitable polyisocyanates are isocyanato-containingpolyurethane prepolymers which can be prepared by reacting polyols withan excess of polyisocyanates and are preferably of low viscosity. It isalso possible to use polyisocyanates containing isocyanurate, biuret,allophanate, iminooxadiazindione, urethane, urea and/or uretdionegroups. Polyisocyanates containing urethane groups, for example, areobtained by reacting some of the isocyanate groups with polyols, such astrimethylolpropane and glycerol, for example. It is preferred to usealiphatic or cycloaliphatic polyisocyanates, especially hexamethylenediisocyanate, dimerized and trimerized hexamethylene diisocyanate,isophorone diisocyanate, 2-isocyanatopropylcyclohexyl isocyanate,dicyclohexylmethane 2,4′-diisocyanate, dicyclohexylmethane4,4′-diisocyanate or 1,3-bis-(isocyanatomethyl)cyclohexane,diisocyanates derived from dimer fatty acids, as sold under thecommercial designation DDI 1410 by Henkel,1,8-diisocyanato-4-isocyanatomethyloctane,1,7-diisocyanato-4-isocyanatomethylheptane or1-isocyanato-2-(3-isocyanatopropyl)-cyclohexane, or mixtures of thesepolyisocyanates.

Very particular preference is given to using mixtures of polyisocyanatescontaining uretdione and/or isocyanurate and/or allophanate groups andbased on hexamethylene diisocyanate, as formed by catalyticoligomerization of hexamethylene diisocyanate using appropriatecatalysts. The polyisocyanate constituent may further comprise anydesired mixtures of the free polyisocyanates exemplified.

The coating composition of the invention may further compriseisocyanato-free crosslinking agents (F′). Depending on their reactivity,these may be present in components (I), (II) and/or (III); the criticalfactor is that the crosslinking agents (F′) do not adversely affect thestorage stability of the component in question, such as by prematurecrosslinking. The skilled worker will therefore be able to select theappropriate combinations of crosslinking agents (F′) on the one hand andcomponents (I), (II) and/or (III) on the other in a simple manner.

Examples of suitable crosslinking agents (F′) are blocked diisocyanatesand/or polyisocyanates based on the aforementioned diisocyanates and/orpolyisocyanates (F). Examples of suitable blocking agents are aliphatic,cycloaliphatic or araliphatic monoalcohols such as methyl, butyl, octylor lauryl alcohol, cyclohexanol or phenylcarbinol; hydroxylamines suchas ethanolamine; oximes such as methyl ethyl ketone oxime, acetone oximeor cyclohexanone oxime; amines such as dibutylamine or diisopropylamine;CH-acidic compounds such as malonic diesters or ethyl acetoacetate;heterocycles such as dimethylpyrazole; and/or lactams such asepsilon-caprolactam. These crosslinking agents (F′) may be present incomponents (I), (II) and/or (III).

Further examples of suitable crosslinking agents (F′) are polyepoxides(F′), especially all known aliphatic and/or cycloaliphatic and/oraromatic polyepoxides, based for example on bisphenol A or bisphenol F.Examples of suitable polyepoxides (F′) also include the polyepoxidesavailable commercially under the designations Epikote® from Shell,Denacol® from Nagase Chemicals Ltd., Japan, such as Denacol EX-411(pentaerythritol polyglycidyl ether), Denacol EX-321 (trimethylolpropanepolyglycidyl ether), Denacol EX-512 (polyglycerol polyglycidyl ether),and Denacol EX-521 (polyglycerol polyglycidyl ether). These crosslinkingagents (F′) may be present in components. (I) and/or (III).

As crosslinking agents (F′) it is also possible to usetris(alkoxycarbonylamino)triazines of the formula

These crosslinking agents (F′) may be present in components (I) and/or(III).

Examples of suitable tris(alkoxycarbonylamino)triazines (F′) aredescribed in the patents U.S. Pat. No. 4,939,213, U.S. Pat. No.5,084,541, and EP-A-0 624 577. The tris(methoxy-, tris(butoxy- and/ortris(2-ethylhexoxycarbonylamino)-triazines are used in particular.

The methyl butyl mixed esters, the butyl 2-ethylhexyl mixed esters, andthe butyl esters are of advantage. They have the advantage over thestraight methyl ester of better solubility in polymer melts, and alsohave less of a tendency to crystallize out.

In particular it is possible to use amino resins, examples beingmelamine resins, as crosslinking agents (F′). In this context it ispossible to use any amino resin suitable for transparent topcoatmaterials or clearcoat materials, or a mixture of such amino resins.Particularly suitable are the customary and known amino resins some ofwhose methylol and/or methoxymethyl groups have been defunctionalized bymeans of carbamate or allophanate groups. Crosslinking agents of thistype are described in the patents U.S. Pat. No. 4,710,542 and EP-B-0 245700 and also in the article by B. Singh and coworkers,“Carbamylmethylated Melamines, Novel Crosslinkers for the CoatingsIndustry” in Advanced Organic Coatings Science and Technology Series,1991, Volume 13, pages 193 to 207. These crosslinking agents (F′) may bepresent in components (I) and/or (III).

Further examples of suitable crosslinking agents (F′) arebeta-hydroxyalkylamides such asN,N,N′,N′-tetrakis-(2-hydroxyethyl)adipamide orN,N,N′,N′-tetrakis(2-hydroxypropyl)adipamide. These crosslinking agents(F′) may be present in components (I) and/or (III).

Further examples of suitable crosslinking agents (F′) are siloxanes,especially siloxanes containing at least one trialkoxy- ordialkoxysilane group. These crosslinking agents (F′) may be present incomponents (I), (II) and/or (III).

The polyisocyanates (F) are used advantageously in an amount of at least70% by weight, with particular preference in an amount of 80 to 100% byweight, based on the overall weight of the crosslinking agents (F) and(F′) in the coating composition of the invention.

The constituents (G) and (H) of component (II) correspond to theabove-described constituents (C) and (E) of component (I), except thathere constituents are used which do not react with isocyanate groups.

To prepare the coating compositions of the invention it is preferred touse components (II) which consist of

(F) from 50 to 100% by weight, preferably from 60 to 90% by weight, ofat least one crosslinking agent,

(G) from 0 to 50% by weight, preferably from 10 to 40% by weight, of atleast one organic, optionally water-dilutable solvent, and

(H) from 0 to 20% by weight, preferably from 0 to 10% by weight, of atleast one customary auxiliary and/or (coatings) additive,

the sum of the weight fractions of components (P) to (H) being in eachcase 100% by weight.

The further key constituent of the coating composition of the inventionis component (III).

In accordance with the invention, this component (III) consists of orcomprises water. It is of advantage in accordance with the invention ifthe component (III) includes further suitable constituents in additionto water. It is substantially free of acrylate copolymers (A) dispersedor dissolved in it.

Examples of suitable constituents are the binders (A) described indetail above, especially the binders (A) containing

(i) functional groups which can be converted into cations byneutralizing agents and/or quaternizing agents, and/or cationic groups,

or

(ii) functional groups which can be converted into anions byneutralizing agents, and/or anionic groups,

and/or

(iii) nonionic hydrophilic groups,

with the exception of acrylate copolymers (A).

Of these binders (A), the binders (A2) and/or (A3) and, whereappropriate, (A4) dispersed or dissolved in water are particularlyadvantageous and therefore used with particular preference.

Where component (I) includes binders (A) which are not, or not to anygreat extent, soluble or dispersible in water, it is advisable to use inparticular the binders (A2) and/or (A3) that are dispersed or dissolvedin water.

Alternatively, the binders (A) may be in the form of a powder slurry. Inthis case flame retardants (F′) may also be present in the powder slurryparticles. Powder slurries are customary and known and are described,for example, in the patents EP-A-0 652 264, U.S. Pat. No. 4,268,542,DE-A-196 13 547, and DE-A-195 18 392.

The component (III) may further comprise at least one of theabove-described reactive diluents.

For preparing the coating compositions of the invention it is veryparticularly preferred to use components (III) which consist of

(J) from 40 to 90% by weight, preferably from 50 to 85% by weight, ofwater,

(K) from 5 to 50% by weight, preferably from 10 to 45% by weight, of thebinder (A), especially the polymeric or oligomeric resins (A2) and/or(A3) and, where appropriate (A4), in a form dissolved or dispersed inwater,

(L) from 0 to 20% by weight, preferably from 2 to 10% by weight, of atleast one neutralizing agent, and

(M) from 0 to 20% by weight, preferably from 2 to 10% by weight, of atleast one customary auxiliary and/or (coatings) additive,

the sum of the weight fractions of components (J) to (M) being in eachcase 100% by weight.

The constituents (L) and (M) of component (III) correspond to theconstituents (D) and (E) of component (I), described above.

The component (III), consisting of an aqueous dispersion of the binders(A) and particularly of the binders (A2) and/or (A3) and, whereappropriate, (A4), may on the one hand be prepared by preparing thebinders (A) in organic solvents, then neutralizing the acid groups,especially carboxyl groups, with the neutralizing agent (L) and,finally, introducing the neutralized constituents into deionized water,or on the other hand may be prepared by emulsion polymerization of themonomeric building blocks of the binders (A) in water.

Preferably, the components (A2) and/or (A3) and, where appropriate, (A4)are first prepared in organic solvents, then neutralized and, finally,dispersed in water in neutralized form.

Examples of suitable neutralizing agents (L) are the ammonia, ammoniumsalts and amines (constituent (D) of component (I)) already described inconnection with the preparation of component (I), it being possible forthe neutralization to take place in organic phase or in aqueous phase.The total amount of neutralizing agent (L) used to neutralizethe-binders (A) is chosen so that from 1 to 100 equivalents, preferablyfrom 50 to 90 equivalents, of the acid groups of the binders (A) areneutralized.

Furthermore, the coating composition of the invention may, based on itsoverall amount, contain up to 40% by weight of constituents (N) whichare curable with. actinic light, especially UV radiation, and/orelectron beams. These constituents may be present in component (I), (II)and/or (III), in particular in component (I). This has the advantagethat the coating compositions of the invention are thermally curableand/or radiation-curable

Suitable constituents (N) include in principle all low molecular mass,oligomeric, and polymeric compounds which are curable with actinic lightand/or electron beams, such compounds being those as are commonly usedin the field of UV-curable or electron-beam-curable coatingcompositions. These radiation-curable coating compositions normallyinclude at least one, preferably two or more, radiation-curable binders,based in particular on ethylenically unsaturated prepolymers and/orethylenically unsaturated oligomers, optionally one or more reactivediluents, and optionally one or more photoinitiators.

It is advantageous to use the radiation-curable binders as constituents(N). Examples of suitable radiation-carable binders (N) are(meth)acryloyl-functional (meth)acrylic copolymers, polyether acrylates,polyester acrylates, unsaturated polyesters, epoxy acrylates, urethaneacrylates, amino acrylates, melamine acrylates, silicone acrylates, andthe corresponding methacrylates. It is preferred to use binders (N)which are free from aromatic structural units. Preference is thereforegiven to using urethane (meth)acrylates and/or polyester(meth)acrylates, with particular preference aliphatic urethaneacrylates.

To prepare the coating compositions, components (I), (II), (III) and(IV) are used preferably in amounts such that the equivalents ratio ofisocyanate-reactive groups of the binders (A) and of the reactivediluents to the crosslinking groups of the crosslinking agent (F) andalso, where appropriate, (F′) is situated between 1:2 and 2:1,preferably between 1:1.2 and 1:1.5.

Furthermore, the coating compositions of the invention preferablycomprise in total

from 15 to 60% by weight, preferably from 20 to 50% by weight, ofbinders (A),

from 5 to 30% by weight, preferably from 10 to 20% by weight, ofcrosslinking agents (F),

from 3 to 25% by weight, preferably from 10 to 20% by weight, of organicsolvents (C),

from 25 to 60% by weight, preferably from 30 to 50% by weight, of water,

from 0 to 50% by weight, preferably from 0 to 30% by weight, of pigmentsand/or fillers (B),

from 0 to 10% by weight of customary coatings additives (E), and

from 0 to 40% by weight, preferably from 0 to 30% by weight, ofconstituents (N) curable with actinic light, especially UV radiation,and/or electron beams,

based in each case on the overall weight of the coating composition ofthe invention.

The preparation of component (I) takes place in accordance with methodsknown to the skilled worker by mixing and, where appropriate, dispersingof the individual constituents. For example, color pigments (B) arenormally incorporated by grinding (dispersing) the respective pigmentsin one or more binders. The dispersing of the pigments takes place withthe aid of customary apparatus, such as bead mills and sand mills, forexample.

Components (II) and (III) and, where appropriate, (V) are likewiseprepared in accordance with methods well known to the skilled worker, bymixing and/or dispersing the individual constituents.

The coating compositions of the invention are prepared in particular bythe following mixing method from components (I), (II), (III) and (IV):

In a first process step, at least one component (I) is mixed with atleast one component (II) to give the mixture (I/II). In a second processstep, at least one component (III) is mixed with at least one component(IV) to give the mixture (III/IV). In a third process step, either themixture (I/II) is dispersed and/or dissolved in the mixture (III/IV) orthe mixture (III/IV) is dispersed and/or dissolved in the mixture(I/II).

In this process, the neutralizing agent (L) may already be present incomponents (I), (III) and/or (IV), or may be added to the mixtures(I/II) and/or (III/IV) or to the coating composition (I/II/III/IV) ofthe invention.

If binders (A) containing exclusively nonionic hydrophilic groups (iii)are used, the use of the neutralizing agents (L) is omitted.

The coating compositions of the invention may be applied to any desiredsubstrates, such as metal, wood, plastic, glass or paper, for example,by customary application methods, such as spraying, knife coating,brushing, flow coating, dipping or rolling, for example.

When used in automotive refinish, the coating compositions of theinvention are normally cured at temperatures below 120° C., preferablyat temperatures of not more than 80° C. When they are used in automotiveOEM finishing it is also possible to employ higher curing temperatures.

The coating compositions of the invention are preferably used to producetopcoats. The coating compositions of the invention may be used both inthe OEM finishing and in the refinish of automobile bodies. However,they are preferably used in the area of refinish and the finishing ofplastics parts.

The aqueous coating compositions of the invention may be used asprimer-surfacers and also to produce singlecoat topcoats, and also aspigmented basecoat materials or, in particular, as clearcoat materialsin a process for producing a multicoat system (basecoat/clearcoatprocess).

EXAMPLES Preparation Example 1

The Preparation of a Polyacrylate Resin (A1)

25 kg of ethoxyethyl propionate (EEP) were weighed into a 100 kilogramsteel reactor suitable for polymerization and equipped with monomerfeed, initiator feed, temperature measurement means, oil heating andreflux condenser, and were heated to 130° C. A mixture of 7.13 kg ofbutyl methacrylate, 5.72 kg of methyl methacrylate, 5.96 kg of styrene,3.16 kg of lauryl methacrylate and 6.76 kg of hydroxyethyl acrylate wasmetered in at a uniform rate with stirring over the course of fourhours. The initiator feed was started five minutes before this feed. Theinitiator solution (2.74 kg of tert-butyl peroxyethylhexanoate in 4.48kg of EEP) was metered in at a uniform rate over 4.5 hours. After 2.5hours of the metering time of the first monomer feed, the second monomerfeed was started. It consisted of 2.8 kg of hydroxyethyl acrylate, 1.36kg of acrylic acid and 0.68 kg of EEP and was metered in at a uniformrate over 1.5 hours.

This gave the polyacrylate resin (A1) having a solids content of 79.2%(one hour; 130° C.), an acid number of 31.1 mg KOH/g and a viscosity of4.4 dPas (55% in EEP).

Preparation Example 2

The Preparation of a Polyester Resin Precursor

A 4 liter steel reactor suitable for polycondensation reactions wascharged with 1088 g of neopentyl glycol hydroxypivalate, 120 g ofphthalic anhydride, 1268 g of isophthalic acid, 21 g ofbutylethylpropanediol, 489 g of neopentyl glycol and 113 g of xylene.This initial charge was then heated and the water of condensation wasremoved continuously until an acid number of 3.5 mg KOH/g was reached.Thereafter a solids content of 79.7% was set using EEP. The acid numberof the resulting polyester resin (A2) was 4.4 mg KOH/g, its viscosity3.6 dpas (60% in EEP).

Proparation Example 3

The Preparation of a Water-dispersed Polyurethane Resin (A3) for use inAccordance With the Invention

A 4 liter steel reactor suitable for polyurethane resin synthesis wascharged with 749 g of the polyester resin precursor from preparationexample 2, 6.6 g of ethylbutylpropanediol, 69 g of dimethylolpropionicacid and 318 g of m-tetramethylxylylene diisocyanate and this initialcharge was left to react at a product temperature of 110° C. until aconstant isocyanate content was reached. Then 101 g oftrimethylolpropane were added in one portion and heating was continueduntil the reaction was ended. Subsequently 31.5 g of EEP were added.After stirring for 30 minutes, the product was neutralized with 36.7 gof dimethylethanolamine. The resultant polyurethane resin (A3) wasdispersed at from 90 to 110° C. in 1929.2 g of water whose temperaturewas 60° C. The resultant dispersion was free from gel particles, washomogeneous, and had a solids content of 36.1%, an acid number of 30.3mg KOH/g, and a pH of 7.1. The dispersions were stable on storage at 40°C. for longer than four weeks.

Example 1

Preparation of an Inventive Coating Composition

1.1 The Preparation of Component (I)

Component (I) was prepared by mixing the following constituents with oneanother using a stirrer (600 rpm):

14 parts by weight of the polyacrylate resin (A1) from preparationexample 1,

3.6 parts by weight of butyl glycol acetate,

3.0 parts by weight of butyl glycol,

1.0 part by weight of a commercial wetting agent (Tensid S fromBiesterfeld),

0.2 part by weight of a leveling agent based on a polyether-modifieddimethylsiloxane copolymer (Byk®331 from Byk Gulden), and

0.6 part by weight of a fluorine-containing leveling agent (Fluorad® FC430, 10% in butyl glycol acetate, from 3 M).

1.2 The Preparation of Component (II)

Component (II) was prepared by mixing 2.9 parts by weight of Desmodur®VPLS 2102 (polyisocyanate of the hexamethylene diisocyanate allophanatetype having an isocyanate content of 20% and a viscosity of less than400 mpas; from Bayer), 10.7 parts by weight of Tolonate HDTLV(polyisocyanate of the hexamethylene diisocyanate isocyanurate typehaving an isocyanate content of 22.5% and a viscosity of less than 2000mPas; from Rhone-Poulenc) and 1.6 parts by weight of ethoxyethylpropionate with one another.

1.3 The Preparation of Component (III)

Component (III) was prepared by mixing 34.5 parts by weight of deionizedwater, 0.45 part by weight of dimethylethanolamine, 1.9 parts by weightof a commercial defoamer (Dapral® T210; from Akzo) and 17.5 parts byweight of the polyurethane resin dispersion (A3) from preparationexample 3 with one another.

1.4 The Preparation of Component (IV) for inventive use

The polyacrylate resin (A1) was prepared in a 4-liter steel reactorequipped with stirrer, reflux condenser, 2 monomer feeds and oneinitiator feed. 385 g of n-butanol were introduced as initial charge andheated to 110° C. Over the course of five hours, a mixture of 255 g ofbutyl methacrylate, 197 g of methyl methacrylate, 181 g of styrene, 113g of Methacrylester 13 (alkyl methacrylate from Rohm & Haas) and 215 gof hydroxyethyl acrylate was metered in. After 3.5 hours of the firstmonomer feed, a second monomer feed consisting of 113 g of hydroxyethylmethacrylate and 58 g of acrylic acid was started and was metered in ata uniform rate over the course of 1.5 hours. Subsequently,polymerization was continued for two hours. Following neutralizationwith 63 g of dimethylethanolamine, the product was stirred for a further30 minutes. The resulting neutralized polyacrylate resin (A1-2) wasdispersed in 1338 g of deionized water. The organic solvent wasdistilled off under reduced pressure to a residual content <1.5%. Afterthe solids content had been adjusted to 39.9% using deionized water, theresulting dispersion was characterized. Its pH was 7.2, its acid number41.4 mg KOH/g. It exhibited pseudoplasticity.

When handled carefully and properly, or under test conditions, thedispersion was stable on storage at 40° C. for longer than four weeks;under operating conditions and/or in transit, however, there werefrequent instances of infestation by microorganisms, so making thedispersion unusable.

Using a disk atomizing dryer, therefore, the dispersion was convertedinto a dry, finely divided solid polyacrylate (A1) whose glasstransition temperature was +52° C. The finely divided solid polyacrylate(A1) was of virtually unlimited storability, without any infestation bymicroorganisms. Even after months of storage, it could be used withoutrestriction for the preparation of inventive coating compositions.

1.5 The Preparation of the Inventive Clearcoat Material

The inventive clearcoat material was prepared in a first process step bymixing the above-described components (I) and (II) with one another,with stirring, with component (II) being stirred into component (I).This gave the mixture (I/II).

In a second process step, component (IV) was dissolved or dispersed incomponent (III), to give the mixture (III/IV).

In a third process step, the mixture (I/II) was added with stirring tothe mixture (III/IV), thereby giving the inventive clearcoat material.

For application, the inventive clearcoat material was adjusted to aviscosity of 35 s (DIN 4 cup) by adding water.

1.6 The Production of Inventiv Coatings and test Panels

Steel panels which had been coated conventionally with anelectrodeposition coating material and a primer-surfacer were coatedwith a black basecoat material in a thickness of from 12 to 15 μm. Thebasecoat was dried at 80° C. for ten minutes. Subsequently the inventiveclearcoat material was applied at different film thicknesses.

Thereafter, the steel panels were dried at room temperature for 15minutes and at 60° C. for 10 minutes and then baked at 140° C.

The leveling of the clearcoat material was outstanding, as was theoverall appearance.

The popping limit was about 60 μm; only a few fine pinholes occurred.

The gloss at 20° in accordance with DIN 67530 was found to be 87.

The gray haze was measured using the Microgloss Haze hazemeter fromByk-Gardner; the figure was below 20.

The gasoline resistance was tested as follows: the coated test panelswere dried in air at 23° C. for 24 hours. Then filter pads with adiameter of 2.3 cm were placed on the test panels. Using a pipette, 0.75ml of super-grade gasoline (not older than four weeks) was trickled ontothe filter pads, followed immediately by the application of 100 gweights. After five minutes, the weights and the filter pads wereremoved. The excess gasoline was removed and the exposure sites wereimmediately examined for marks. There were no marks to be seen.

What is claimed is:
 1. A system of at least four components for acoating composition comprising, (I) a component comprising at least oneolegomeric or polymeric resin containing functional groups that reactwith isocyanate groups as binder, (II) a component comprising at leastone polyisocyanate as crosslinking agent, (III) a component thatcomprises water and is substantially free from acrylate copolymersdispensed or dissolved therein, and (IV) a finely divided solidcomponent that comprises at least one water-soluble or dispersiblefinely divided solid acrylate copolymer wherein the at least fourcomponents are not mixed.
 2. The system of at least four components fora coating composition of claim 1, wherein the finely divided solidcomponent (IV) is prepared by at least one of i) spray-drying solutions,emulsions, or dispersions of the acrylate copolymers; ii) freeze-dryingof solutions, emulsions, or dispersions of the acrylate copolymers; iii)precipitation of acrylate copolymers from their solution, dispersion oremulsion; iv) emulsion polymerization of the acrylate copolymers; v)precipitation polymerization of the acrylate copolymers; and vi)grinding of the acrylate copolymers.
 3. The system of at least fourcomponents for a coating composition of claim 1, wherein the functionalgroups that react with isocyanate groups comprise hydroxyl groups. 4.The system of at least four components for a coating composition ofclaim 1, wherein component (III) further comprises at least one binder.5. The system of at least four components for a coating composition ofclaim 1, wherein at least one of i) component (I) comprises at least onewater-soluble or -dispersible binder, and ii) component (III) comprisesat least one water-dissolved or water-dispersed binder.
 6. The system ofat least four components for a coating composition of claim 5, whereinthe binders comprises at least one of (i) functional groups that can beconverted into cations by at least one of neutralizing agents andquaternizing agents, (ii) functional groups that are cationic groups,(iii) functional groups that can be converted into anions byneutralizing agents (iv) functional groups that are anionic groups, and(v) nonionic hydrophilic groups.
 7. The system of least four componentsfor a coating composition of claim 6, wherein the binders contain atleast one of carboxylic acid groups and carboxylate groups.
 8. Thesystem of at least four components for a coating composition of claim 7,wherein component (I) comprises at least one of the following as binders(A1) at least one acrylate copolymer that is dispersible or soluble inone or more organic, optionally water-dilutable solvents, containshydroxyl groups and at least one of carboxylic acid groups andcarboxylate groups, and has a number average molecular weight Mn ofbetween 1000 and 30,000 daltons, an OH number of from 40 to 200 mgKOH/g, and an acid number of from 5 to 150 mg KOH/g, (A2) at least onepolyester resin that is dispersible or soluble in one or more organic,optionally water-dilutable solvents, contains hydroxyl groups at leastone of carboxylic acid groups and carboxylate groups, and has a numberaverage molecular weight Mn of between 1000 and 30,000 daltons, an OHnumber of from 30 to 250 mg KOH/g, and an acid number of from 5 to 150KOH/g, and (A3) at least one polyurethane resin that is dispersible orsoluble in one or more organic, optionally water-dilutable solvents,contains hydroxyl groups and at least one of carboxylic acid groups andcarboxylate groups, and has a number average molecular weight Mn ofbetween 1000 and 30,000 daltons,an OH number of from 20 to 200 mg KOH/g,and an acid number of from 5 to 150 mg KOH/g; and component (III)comprises as binders at least one of the polyester resins (A2) and thepolyurethane resins (A3), and component (IV) comprises as binder theacrylate copolymer (A1).
 9. The system of at least four components for acoating composition of claim 4, wherein some of the binders in component(III) are powder slurry particles.